NEET Exam > NEET Notes > Short Notes > Short Notes Breathing and Exchange of Gases - Short Notes for NEET
Short Notes Breathing and Exchange of Gases - Short Notes for NEET
Respiratory Organs in Animals
| Organism/Group | Respiratory Organ |
|---|---|
| Protozoa, Sponges, Coelenterates | Body surface (diffusion) |
| Earthworm | Moist skin |
| Insects | Tracheal system |
| Aquatic arthropods, Molluscs | Gills |
| Fishes | Gills |
| Amphibians | Skin, Gills (larval), Lungs (adult) |
| Reptiles, Birds, Mammals | Lungs |
Human Respiratory System
Parts of Respiratory System
| Part | Structure & Function |
|---|---|
| Nostrils | External openings; contain hair to filter air |
| Nasal chamber | Lined with mucus and cilia; warms, moistens, and filters air |
| Pharynx | Common passage for food and air |
| Larynx | Voice box; contains vocal cords; made of cartilage |
| Trachea | Windpipe; supported by C-shaped cartilaginous rings; prevents collapse |
| Bronchi | Trachea divides into right and left primary bronchi; enter respective lungs |
| Bronchioles | Fine branches of bronchi within lungs; terminate in alveoli |
| Alveoli | Grape-like air sacs; site of gaseous exchange; ~300 million per lung Thin-walled, surrounded by capillaries |
Lungs
- Location: Thoracic cavity; surrounded by ribs, sternum, and diaphragm
- Number: Two (right and left)
- Right lung: 3 lobes
- Left lung: 2 lobes (cardiac notch present)
- Pleura:Double-layered membrane covering lungs
- Outer parietal pleura
- Inner visceral pleura
- Pleural fluid between layers reduces friction
- Lungs are spongy, elastic due to presence of alveoli and connective tissue
Mechanism of Breathing
Inspiration (Inhalation)
- Active process
- External intercostal muscles contract → ribs and sternum move upward and outward
- Diaphragm contracts → moves downward (flattens)
- Thoracic volume increases
- Pulmonary (intra-alveolar) pressure decreases below atmospheric pressure
- Air rushes into lungs
Expiration (Exhalation)
- Passive process (normally)
- Internal intercostal muscles contract → ribs and sternum move downward and inward
- Diaphragm relaxes → moves upward (dome-shaped)
- Thoracic volume decreases
- Pulmonary pressure increases above atmospheric pressure
- Air is expelled from lungs
Respiratory Volumes and Capacities
| Volume/Capacity | Value (approx.) | Definition |
|---|---|---|
| Tidal Volume (TV) | 500 mL | Volume of air inspired or expired during normal breathing |
| Inspiratory Reserve Volume (IRV) | 2500-3000 mL | Additional air that can be forcibly inspired after normal inspiration |
| Expiratory Reserve Volume (ERV) | 1000-1100 mL | Additional air that can be forcibly expired after normal expiration |
| Residual Volume (RV) | 1100-1200 mL | Air remaining in lungs after forceful expiration; cannot be expelled |
| Inspiratory Capacity (IC) | 3000-3500 mL | TV + IRV |
| Expiratory Capacity (EC) | 1500-1600 mL | TV + ERV |
| Functional Residual Capacity (FRC) | 2100-2300 mL | ERV + RV |
| Vital Capacity (VC) | 3500-4500 mL | IRV + TV + ERV; maximum air expired after maximum inspiration |
| Total Lung Capacity (TLC) | 5000-6000 mL | VC + RV; total volume of air lungs can hold |
Additional Respiratory Parameters
- Minute Respiratory Volume: TV × Respiratory rate = 500 mL × 12-16 = 6000-8000 mL/min
- Dead space air: ~150 mL (air in conducting zone that doesn't participate in gas exchange)
- Spirometer: Instrument used to measure respiratory volumes
Exchange of Gases
Mechanism
- Occurs by simple diffusion
- Driven by pressure/concentration gradient
- Diffusion rate depends on:
- Partial pressure gradient
- Solubility of gas
- Thickness of membrane
- Surface area available
Partial Pressures (in mm Hg)
| Location | pO₂ | pCO₂ |
|---|---|---|
| Atmospheric air | 159 | 0.3 |
| Alveolar air | 104 | 40 |
| Deoxygenated blood (pulmonary artery) | 40 | 45 |
| Oxygenated blood (pulmonary vein) | 95 | 40 |
| Tissues | 40 | 45 |
Sites of Gas Exchange
- External respiration:Between alveoli and blood (pulmonary capillaries)
- O₂ diffuses from alveoli (pO₂=104) to blood (pO₂=40)
- CO₂ diffuses from blood (pCO₂=45) to alveoli (pCO₂=40)
- Internal respiration:Between blood and tissue cells
- O₂ diffuses from blood (pO₂=95) to tissues (pO₂=40)
- CO₂ diffuses from tissues (pCO₂=45) to blood (pCO₂=40)
Transport of Gases
Oxygen Transport
- 97% transported as oxyhaemoglobin(HbO₂)
- Hb + 4O₂ ⇌ Hb(O₂)₄
- Each Hb molecule binds 4 O₂ molecules
- 3% dissolved in plasma (physical solution)
- Oxygen-Haemoglobin Dissociation Curve:S-shaped (sigmoid)
- Shows relationship between pO₂ and % saturation of Hb
- At alveoli (high pO₂): Hb binds O₂
- At tissues (low pO₂): Hb releases O₂
Factors Affecting Oxygen Binding
- pO₂: Higher pO₂ → increased binding
- pCO₂: Higher pCO₂ → decreased O₂ binding (Bohr effect)
- H⁺ concentration: Lower pH → decreased O₂ binding
- Temperature: Higher temperature → decreased O₂ binding
Carbon Dioxide Transport
- 7% dissolved in plasma
- 23% as carbamino-haemoglobin(bound to Hb)
- CO₂ binds to amino groups of Hb
- 70% as bicarbonate ions (HCO₃⁻)in plasma
- CO₂ + H₂O ⇌ H₂CO₃ (catalyzed by carbonic anhydrase in RBCs)
- H₂CO₃ ⇌ H⁺ + HCO₃⁻
- HCO₃⁻ diffuses into plasma
- Cl⁻ enters RBC to maintain ionic balance (Chloride shift/Hamburger shift)
Regulation of Respiration
Respiratory Rhythm Center
- Located in medulla oblongata of brain
- Inspiratory center: Activates inspiration
- Expiratory center: Activates expiration (during forceful breathing)
- Pneumotaxic center (in pons): Regulates duration and rate; inhibits inspiration
Chemosensitive Area
- Located adjacent to respiratory center in medulla
- Sensitive to CO₂ and H⁺ ions
- Increase in CO₂ or H⁺ → activates respiratory center → increases rate and depth
Peripheral Chemoreceptors
- Aortic bodies (in aortic arch)
- Carotid bodies (at bifurcation of carotid artery)
- Sensitive to O₂, CO₂, and H⁺
- Signal respiratory center when levels change significantly
Other Factors
- Stretch receptors in alveoli prevent over-inflation (Hering-Breuer reflex)
- Voluntary control: Cerebral cortex can override automatic control temporarily
Disorders Related to Respiration
| Disorder | Description | Causes/Features |
|---|---|---|
| Asthma | Difficulty in breathing; inflammation of bronchi and bronchioles | • Allergens (dust, pollen, smoke) • Bronchial constriction • Excessive mucus production • Wheezing sound during breathing |
| Emphysema | Chronic disorder; alveolar walls damaged | • Cigarette smoking (major cause) • Reduced respiratory surface • Difficulty in expiration • Barrel-shaped chest |
| Occupational Respiratory Disorders | Caused by inhaling harmful particles at workplace | • Silicosis: Silica dust (mining, stone cutting) • Asbestosis: Asbestos fibers • Black lung disease: Coal dust • Fibrosis of lung tissue |
Additional Disorders (Brief)
- Pneumonia: Infection causing inflammation of alveoli; fluid accumulation
- Tuberculosis (TB): Bacterial infection (Mycobacterium tuberculosis); lung damage
- COPD (Chronic Obstructive Pulmonary Disease): Group of diseases including chronic bronchitis and emphysema
- Bronchitis: Inflammation of bronchi; excessive mucus
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FAQs on Short Notes Breathing and Exchange of Gases - Short Notes for NEET
| 1. What is the process of breathing? |  |
Ans. Breathing is the physical process by which organisms inhale oxygen and exhale carbon dioxide. It involves two main phases: inhalation, where air enters the lungs, and exhalation, where air is expelled. This process is essential for gas exchange in the body.
| 2. How does gas exchange occur in the lungs? | |
Ans. Gas exchange in the lungs occurs in the alveoli, tiny air sacs surrounded by capillaries. Oxygen from the inhaled air diffuses through the alveolar walls into the blood, while carbon dioxide from the blood diffuses into the alveoli to be exhaled. This exchange is driven by the concentration gradients of the gases.
| 3. What role do the diaphragm and intercostal muscles play in respiration? | |
Ans. The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. When it contracts, it flattens, increasing the volume of the thoracic cavity and drawing air into the lungs. The intercostal muscles assist by expanding and contracting the rib cage, further aiding the inhalation and exhalation processes.
| 4. What is the significance of oxygen and carbon dioxide in cellular respiration? | |
Ans. Oxygen is vital for cellular respiration, a process where cells convert glucose into energy (ATP). During this process, oxygen is used to break down glucose, producing carbon dioxide as a waste product. This carbon dioxide is then transported back to the lungs for exhalation, maintaining a balance of gases in the body.
| 5. What factors can affect the rate of breathing? | |
Ans. Several factors can influence the rate of breathing, including physical activity, emotional state, and environmental conditions. During exercise, the body requires more oxygen, leading to an increased breathing rate. Stress and anxiety can also elevate the rate of breathing, while high altitudes may cause the body to adapt by increasing respiration to compensate for lower oxygen levels.
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